﻿using System;

class Circle
{
    private const double PI = Math.PI;

    public static double Area(double r)
    {
        return r * r * PI;
    }

    public static double Perimeter(double r)
    {
        return 2 * PI * r;
    }
}
class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("输入圆的半径：");
        double r=Convert.ToDouble(Console.ReadLine());

        Console.WriteLine($"圆的周长：{r} * 2 * π = {Circle.Perimeter(r):F2}");
        Console.WriteLine($"圆的面积：{r} * {r} * π = {Circle.Area(r):F2}");
    }
}